Cancer is responsible for a quarter of all deaths in the United States. Breast cancer is projected to cause 458,000 deaths with 1,383,000 new cases worldwide in 2012. Breast cancer is also estimated to include 29% of all new cancer cases in women in the United States during 2012, resulting in 14% of cancer related deaths. Early detection and improved treatment have increased breast cancer survival rates in the United States over the past two decades. While proton (1H) magnetic resonance imaging (MRI) is used for cancer detection due to its improved sensitivity when compared to mammography and ultrasound, 1H-MRI suffers from intermediate specificity which can result in false positive studies leading to unnecessary interventions. Because sodium (23Na) concentration is known to increase in malignant lesions when compared to surrounding healthy tissues, 23Na-MRI may be able to improve specificity, potentially improving evaluation and assessment of breast lesions. Sodium MRI shows promise in characterizing and assessing tumor viability, cartilage health, renal failure, tissue damage following stroke, and multiple sclerosis. However, in comparison with conventional 1H-MRI, 23Na-MRI is challenging due to relatively low 23Na concentrations in biological tissues, rapid bi-exponential signal decay, and a low gyromagnetic ratio. Despite these challenges, recent improvements in coil and gradient hardware, the availability of whole-body scanners with high polarizing field strengths, and the development of more efficient pulse sequences have spurred renewed interest in 23Na-MRI. These advances have enabled the acquisition of higher quality in vivo 23Na-MRI images than previously possible, often within clinically reasonable scan times. While 23Na-MRI has become more promising, there is still a need for improved image quality and signal-to-noise ratio (SNR) to make quantitative 23Na-MRI feasible for many of the clinical applications under consideration.
Phased array coils can be used to improve the SNR of 23Na-MRI. This is achieved through simultaneous data acquisition from multiple surface coils which have inherently increased signal sensitivity and limited noise volume by being placed in close proximity to the object or anatomy of interest. Specifically designed coil arrays also allow reductions in image acquisition time through the application of parallel imaging techniques. Phased array coil concepts have been extensively applied to 1H-MRI coil design, routinely providing improved SNR and accelerated image acquisition compared to that provided by volume coils or other large coils of similar area. However, phased arrays have not been widely used in non-proton imaging, and typically require sophisticated custom hardware for implementation on commercial scanners. Despite these challenges, sites with the capability to support multi-channel non-proton receivers are becoming increasingly common. The first reported non-proton phased array was built for phosphorous imaging in 1992 almost a decade before the first reported 23Na array at 1.5T in 2000. In the past few years, there has been a substantial increase in the number of 23Na coil arrays developed for 3T, 4T, and 7T. Some of these array configurations are dual resonant, with the ability to image 1H and 23Na without repositioning the subject
The preferred embodiment of the present invention is a new dual resonant breast coil design consisting of a 7-channel 23Na receive array, a larger 23Na transmit coil, and a 4-channel 1H transceive array. The new composite array design utilizes smaller 23Na receive loops than those typically used in 23Na imaging. Novel methods are also employed to decouple the receive loops from the transmit loops. A novel multi-channel 1H transceive coil is superimposed on the 23Na receive array, and decoupling between 1H and 23Na elements is achieved by intersecting the constituent loops to reduce the mutual inductance between the 1H and 23Na arrays. The new design achieves excellent 23Na-SNR over the sensitive volume while also providing good image quality for conventional 1H imaging.
The present invention represents a departure from the prior art in that the MRI coil design of the present invention allows for smaller and more efficient receive loops and a decoupling methodology allowing for good imagery of desired tissues in a shorter period of time for image acquisition. The preferred embodiment in this Specification is a breast coil used to diagnose and locate cancerous lesions in human breast tissue; however, it is to be understood that the concepts and details of the invention may be adapted to create scanning apparatuses and structures for use with any individual component of targeted anatomy. As such, while described in terms of a breast coil, the invention should be understood to include other structures and constructions which may be specific to a desired portion of anatomy other than the human breast.